The invention relates to an integrated semiconductor circuit for rapid switching processes having at least one input and one output and a bipolar transistor operated in an emitter connection between whose collector electrode and base electrode a unidirectional semiconductor element is arranged.
In digital circuit technology, bipolar transistors are advantageously used for switching. Thanks to their high mutual conductance, they can supply a large output current rise with a small input voltage rise.
The dynamic behaviour of bipolar transistors is determined by the change of the stored charges. A transistor operated in the saturation state and having a high stored charge in the base has a retarded switching behaviour. For this reason, saturation of the bipolar transistors must be avoided for rapid switching processes.
In so-called Schottky transistors, saturation is avoided by connecting a Schottky diode parallel to the base-collector barrier layer (See A. Muller, "Bauelemente der Halbleiter-Elektronik", Springer-Verlag, 3rd edition, p. 249 ff.).
Since Schottky diodes have substantially lower threshold voltages than pn-junctions, the current flows predominantly through the Schottky diode in the case of parallel connection, and not through the collector-base junction of the bipolar transistor. Unlike the pn-junction in the transistor, Schottky diodes are majority carrier components in which forward biasing does not lead to additional charge storage, for which reason the switching speed of the array is increased in the case of parallel connection.
In integrated circuit technology, the manufacture of Schottky diodes requires additional process steps, thereby increasing the manufacturing time and also production costs. A further mask must be made to structure the Schottky contact. A further metal must be introduced into the process, since the aluminum used in the usual integration process is not suitable for the Schottky contact. Deposition of the metal entails a photoresist coating process, exposure, development, photoresist etching, and metal etching. Immersion-type doping must be low and precisely checked for a Schottky contact. Since the manufacture of as small as possible structures requires heavy doping, the use of a Schottky diode militates against a structure reduction.